Mix together in a bowl the pork, grapefruit juice, onions, shallots, green peppers and salt. Pour mixture into a ziplock bag and massage. Refrigerate overnight.
Pour the pork mixture into a large pot and simmer at a very low flame for 1 1/2 hours. No need to add water. When the pork is cooked, drain and rinse in a colander, being sure to remove the bits and pieces of onion, pepper, etc. Allow the rinsed pork to dry on a cutting board for about 15-20 minutes.
Heat oil in a wok or black skillet and fry pork to a golden brown. Garnish with sliced green pepper and onion rings.